The display device market is rapidly changing based on flat panel displays (FPDs) that are easy to fabricate over a large area and can be reduced in thickness and weight. Such flat panel displays include liquid crystal displays (LCDs), organic light emitting displays (OLEDs), and electrophoresis devices.
In line with recent efforts to further extend the application and use of flat panel displays, particular attention has focused on so-called flexible display devices in which flexible substrates are applied to flat panel displays. The application of such flexible display devices is particularly reviewed based on mobile devices such as smart phones and the application fields thereof are gradually extended.
Processes for the formation and handling of display device structures such as thin film transistors (TFTs) on plastic substrates (TOP) are important in the fabrication flexible display devices. However, due to the flexibility of flexible substrates included in flexible display devices, many problems still remain in terms of processing when flexible plastic substrates are directly employed in place of existing glass device substrates to form device structures.
Particularly, a thin film glass included in a flexible substrate tends to be brittle when an impact is applied thereto. Due to this tendency, a process for producing a display substrate is carried out in a state in which thin film glass is placed on carrier glass. FIG. 1 schematically illustrates a process for fabricating a device (e.g., a flexible display device) having a flexible substrate according to the prior art.
Referring to FIG. 1, a sacrificial layer 2 composed of a suitable material such as a-silicon is formed on a carrier substrate 1 such as a glass substrate, and a flexible substrate 3 is formed thereon. Thereafter, a device structure such as a thin film transistor is formed on the flexible substrate 3 supported by the carrier substrate 1 in accordance with a conventional process for the fabrication of a device on a glass substrate. Then, laser or light is irradiated onto the carrier substrate 1 to destroy the sacrificial layer 2 and separate the flexible substrate 3 on which the device structure is formed, completing the fabrication of a device (for example, a flexible display device) having the flexible substrate 3.
According to the prior art method, however, the laser or light irradiation affects the device structure, increasing the risk of defects. Further, a system for the laser or light irradiation and a separate process are required, disadvantageously rendering the overall device fabrication process complex and markedly increasing the fabrication cost.
Although not illustrated in FIG. 1, it is often necessary to form an additional adhesive layer between the sacrificial layer 2 composed of a-Si and the flexible substrate 3 due to insufficient adhesion between the sacrificial layer and the flexible substrate. This makes the overall process more complicated and the conditions for laser or light irradiation more severe, which increases the risk that the reliability of the device may be adversely affected.